Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, an inkjet recording apparatus is known that uses a recording head (liquid-droplet ejection head) for ejecting droplets of ink.
Such liquid-ejection-type image forming apparatuses fall into two main types: a serial-type image forming apparatus that forms an image by ejecting droplets from the recording head while moving the carriage with the recording head in a main scanning direction, and a line-head-type image forming apparatus that forms an image by ejecting droplets from a linear-shaped recording head held stationary in the image forming apparatus as the recording medium is conveyed thereto.
For such a liquid-ejection-type image forming apparatus, for example, JP-2009-096126-A proposes a head tank serving as a liquid container. The liquid container includes an air release mechanism to open and close an air release hole for releasing an interior of a container main unit to outside air. The air release mechanism has a gasket member, a spherical member, and an air-release movable member within a cylindrical air release cap. The spherical member is arranged to come into contact with and separate from the gasket member and be movable from the outside of the liquid container. The air-release movable member is disposed at a position close to the outside air relative to the spherical member so as to be movable back and forth and moves the spherical member. The outer circumferential surface of the movable member is held so as to be slidable over an opening of the air release cap. A communication channel communicating with the outside air is formed within the movable member, and a filter member for capturing foreign substances is mounted to the communication channel.
However, as conventionally performed, in a case in which the filter member is mounted to an opening of the communication channel close to the outside air, for example, dust or other foreign substances may enter the communication channel when bonding the filter member onto the communication channel. In such a case, the foreign substances cannot be removed, thus reducing the air tightness of the valve unit. As a result, the air tightness of the liquid container is compromised and air enters the liquid container, thus hampering stable ink supply.